Antebellum states were critical in supporting the emerging rail system of the nineteenth century, yet not all states engaged in active rail promotion efforts. In this analysis, I consider how local economic and political conditions, as well as the rail promotion activities of a state's contiguous neighbors, impacted a legislature's rail promotion decisions. The findings suggest that states only engaged in rail promotion when local infrastructure was of poor quality and a state's tax revenues were sufficient to support rail expenditures. These findings reveal that diffusion, powered by social learning, does not drive all state policy innovations. Instead, local conditions and parallel thinking are important factors in state policy development. Furthermore, the analysis underscores the power of local governments in the antebellum period, while also raising the question of whether such diffuse state building was effective.